Help diagnose this problem

[GreenThumb81]

Hi guys,

Having some slight issues with these young plants.

Mars Hydro 400w LED
Advance Nutrients PH perfect 3 part Nutrients
PH 6.0
Room temp 24-30 degrees C
6" extraction fan with 6"carbon filter
Humidity 30-50%

That's the basic specs for the grow.
Had these guys in coco for a couple weeks then transferred to net pots. They looked like they were slightly under fed with the leaves being a light green colour.

I upped the nutes and it seemed to fix the problem.
They then got a strong growth spurt and as you can see have turned yellow again with some green on the pointy half of the leaf.
I am still dosing under the users recommendation. Trying to feel out what they can handle.
I don't have an EC meter.
I am thinking it may be a nitrogen deficiency. I added more to the reservoir and some cali mag aswell but it hasn't rectified the problem.
The next thing I am going to try Is a reservoir change with a fresh mix.
The light is 80 cm away from the plants. they have a fan blowing on them constantly as well.
Is light bleaching a possibility?

Thanks in advance for any advice, need to sort this out asap

 

[Gardenseed]

From my research the possibility is -Nitrogen deficiency
-Iron Deficiency
-lighting is too far.

Id start with adding a little iron chelate to the solution and bringing my light closer to the plant.